The present invention generally relates to methods and systems for surge detection during the operation of turbomachinery. More specifically, the present invention relates to methods and systems for surge detection during the operation of a gas turbine engine by monitoring the short-term variance of altitude-corrected compressor discharge pressure rate of change.
Turbomachinery, such as gas turbine engines, APUs and certain types of compressors can experience an undesirable operating condition called surge or stall. Surge typically occurs when a compression stage airflow and pressure become mismatched, i.e., not enough airflow for a given pressure ratio (exit pressure/inlet pressure) or too much pressure ratio for a given airflow. Surge disrupts the operation,of the turbomachine. Characteristics of a single pop surge include rapid drops in compressor discharge pressure (CDP), followed by a rapid recovery of CDP. Severe surge events are multiple pop or locked-in surge, where CDP repeatedly falls and recovers, then falls again and recovers, on and on, at rates up to 10 or more times per second. Surge typically causes a momentary or sustained loss of power and can cause mechanical damage to the turbomachinery.
Many turbomachinery control systems attempt to either anticipate an impending surge and initiate corrective action, or detect the initial stages of a current surge condition and take corrective action. Many of the available turbomachinery control systems have limitations such as frequent occurrence of false alarms, measurement of multiple parameters and use various additional components.
U.S. Pat. No. 6,231,306 to Khalid (the ""306 patent) discloses a control system for preventing a compressor stall in a gas turbine engine. The ""306 patent discusses a control system which attempts to detect an impending surge condition in a gas turbine engine and initiates corrective action. The control system of the ""306 patent monitors a normalized magnitude of compressor static pressure fluctuations in a frequency band determined by engine speed In order to detect an impending surge condition. The control system of the ""306 patent utilizes a signal indicative of the amplified low-pressure compressor disturbances in order to predict an impending surge condition.
U.S. Pat. No. 6,059,522 to Gertz et al. (the ""522 patent) discloses techniques for diagnosing and avoiding stall In rotary compressors such as aircraft jet engines. The ""522 patent discusses the use of a control system that measures compressor flow characteristics by placing one or more pressure sensors in the compressor flow pattern, monitoring the magnitude of compressor pressure fluctuations in a frequency range determined by engine speed. The resultant magnitude signals are compared to known values for the compressor in order to indicate stall susceptibility.
U.S. Pat. No. 5,726,891 to Sisson et al. (the ""891 patent) discloses a control system for detecting an occurrence of surge in a gas turbine engine. The method of the ""891 patent obtains filtered derivatives of engine operating characteristics, principally fan speed and exhaust temperature, compares the filtered derivatives to threshold values and increments a count only if both derivatives exceed their respective threshold values. A surge condition is signaled only if the count is equal to a predetermined value.
CDP measurements are commonly used to detect surge. Methods include monitoring for a high rate of change of CDP, a rapid drop in CDP, or rapid drops and recoveries in CDP. Modern turbomachinery control systems monitor CDP pressure, with a bandwidth or sampling rate much higher than that at which the CDP signal changes during operation. This oversampling results in high autocorrelation of CDP (and CDP rate of change) over the short term. Inversely, short-term average signal variance is quite small during normal operation. A surge event causes the short-term autocorrelation to drop dramatically, and causes the short-term variance to soar CDP corrected for altitude (CDP/turbomachine inlet pressure) provides an even better indication of surge.
As can be seen, there is a need for an improved method and system in order to detect surge conditions within turbomachinery. The improved method and system should reduce the occurrence of false alarms, i.e., the Incorrect signaling of surges, and quickly detect severe surge conditions by monitoring minimal engine parameters and using minimal sensing components.
In one aspect of the present invention, a method of surge detection within a turbomachine compressor comprises: measuring a compressor discharge pressure (CDP) of the turbomachine over a period of time: determining a time derivative (CDPD) of the measured (CDP); correcting the CDPD for altitude, (CDPDCOR), inputting CDPDCOR2 into a first filter algorithm (FFA); inputting CDPDCOR into a second filter algorithm (SFA); estimating a short-term average of CDPDCOR2 by using the FFA; estimating a short-term average of CDPDCOR by using the SFA; determining a short-term variance of corrected CDP rate of change (CDProc) based upon the short-term average of CDPDCOR and the short-term average of CDPDCOR2; comparing the short-term variance of CDPDCOR rate of change with a predetermined threshold(CDPproc); signaling an output when CDProc greater than CDPproc; and signaling an occurrence of a surge within the turbomachine compressor when CDProc remains greater than COPproc for pre-determined period of time.
In another aspect of the present invention, a method of surge detection within a turbomachine compressor comprises: measuring the compressor discharge pressure (CDP) of the turbomachine compressor over a period of time; determining a time derivative (CDPD) of the measured (CDP); correcting the CDPD for altitude, (CDPDCOR); estimating a short-term average of CDPDCOR2 by using a first filter algorithm (FFA); estimating a short-term average of CDPDCOR by using the a second filter algorithm (SFA); determining a short-term variance of corrected CDPD (CDPproc) based upon the short-term average of CDPDCOR and the short-term average of CDPDCOR2; comparing the short-term variance of corrected CDP rate of change with a pre-determined short-term variance of CDP rate of change threshold (CDPproc); signaling an output when CDProc greater than CDPproc; and signaling an occurrence of a surge within the turbomachine compressor when CDProc remains greater than CDPproc for predetermined period of time.
In another aspect of the present invention, a method of surge detection within a turomachine compressor comprises: measuring the compressor discharge pressure (CDP) of the turbomachinery compressor over a period of time; determining a time derivative (CDPD) of the measured (CDP); correcting the CDPD for altitude, (CDPDCOR); estimating a short-term average of CDPDCOR2; estimating a short-term average of CDPDCOR; determining a short-term variance of corrected CDP rate of change (CDPD)based upon the short-term average of CDPDCOR and the short-term average of CDPDCOR2; comparing the short-term variance of corrected CDP rate of change with a pre-determined threshold (CDPproc); signaling an output when CDProc greater than CDPproc; and signaling an occurrence of a surge within the turbomachinery compressor when CDProc remains greater than CDPproc for pre-determined period of time.
In another aspect of the present invention, a method of surge detection within a turbomachine compressor comprises: digitally sampling the compressor discharge pressure (CDP) of the compressor over a period of time (Tsample) by using a compressor discharge pressure probe; determining a time derivative (CDPD) of the measured (CDP), where CDPD (n)=(CDP(n)xe2x88x92CDP(nxe2x88x921))/Tsample, CDP(n) and CDP(nxe2x88x921) are the nth and (nxe2x88x921)th sample of CDP respectively and CDPD(n) is the nth sample of CDPD; correcting the CDPD for altitude, (CDPDCOR); inputting CDPDCOR2 into a first filter algorithm (FFA); inputting CDPDCOR into a second filter algorithm (SFA); calculating or estimating a short-term average of CDPDCOR2 (E[CDPDCOR2](n)) by using the FFA which uses a rolling average of the z most recent CDPDCOR2, E[CDPDCOR2](n)=[CDPDCOR2(n)+CDPDCOR2(nxe2x88x921)+CDPDCOR2 (nxe2x88x922) . . . +CDPDCOR2 (nxe2x88x92(zxe2x88x921))]/z or a bilinear transform implementation of a first order lag E[CDPDCOR2](n)=c1*E[CDPDCOR2](nxe2x88x921)+((1xe2x88x92c)1/2)*CDPDCOR2(n)+((1xe2x88x92c1)/2)*CDPDCOR2(nxe2x88x921); calculating or estimating a short-term average of CDPDCOR (E[CDPDCOR](n)) by using the SFA which uses a rolling average of the z most recent CDPDCOR, E[CDPDCOR](n)=[CDPDCOR (n)+CDPDCOR (nxe2x88x921)+CDPDCOR (nxe2x88x922) . . . +CDPDCOR (nxe2x88x92(zxe2x88x921))]/z or a bilinear transform implementation of a first order lag E[CDPDCOR](n)=c1*E[CDPDCOR](nxe2x88x921)+((1xe2x88x92c1)/2)*CDPDCOR(n)+((1xe2x88x92c1)/2)*CDPDCOR(nxe2x88x921); determining a short-term variance of corrected CDP rate of change (Var[CDPDCOR]) based upon E2[CDPDCOR] and E[CDPDCOR2], Var[CDPDCOR]=E[CDPDCOR2]xe2x88x92E2[CDPDCOR]; comparing the short-term variance of corrected CDP rate of change with a pre-determined threshold (CDPproc); signaling an output when Var[CDPDCOR] greater than CDPproc; and signaling an occurrence of a surge within the turbomachine compressor when Var[CDPDCOR] remains greater than CDPproc for pre-determined period of time.
In another aspect of the present invention, a system for surge detection within a turbomachine compressor comprises: a compressor discharge probe that measures the compressor discharge pressure (CDP) of the turbomachine compressor over a period of time; a signal processor that receives the CDP measurements from the compressor discharge probe, determines a time derivative (CDPD) of the measured CDP and corrects the CDPD for altitude, (CDPDCOR); a first filter which receives CDPDCOR2 and performs a first filter algorithm (FFA) that estimates a short-term average of CDPDCOR2; and a second filter which receives CDPDCOR and performs a second filter algorithm (SFA) that estimates a short-term average of CDPDCOR, wherein the signal processor determines a short-term variance of CDPDCOR (CDProc) based upon the short-term average of CDPDCOR and the short-term average of CDPDCOR2; compares the short-term variance of corrected CDP rate of change (CDProc)with a pre-determined threshold (CDPproc); signals an output when CDProc greater than CDPproc; and signals an occurrence of a surge within the turbomachine compressor when CDProc remains greater than CDPproc for pre-determined period of time.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.